Conductivity of the nanostructured ceramic material Zr<Subscript>0.88</Subscript>Sc<Subscript>0.1</Subscript>Ce<Subscript>0.01</Subscript>Y<Subscript>0.01</Subscript>O<Subscript>1.955</Subscript> prepared from mechanically activated powders

The structure of the Zr_0.88 Sc_0.1Ce_0.01Y_0.01O_1.955 solid solution, a candidate for the use as a solid electrolyte in fuel cells with a low temperature, has been investigated using x-ray powder diffraction and Raman spectroscopy. Single-phase ceramic materials have been produced from powders prepared by the mechanochemical synthesis from ZrO₂ nanoprecursors purified of the impurities introduced during grinding of commercial zirconia. The solid solution has a rhombohedral structure at room temperature owing to the partial ordering of oxygen vacancies. The electrical conductivity of the ceramic materials sintered at temperatures below 1570 K exhibits a hysteresis due to the delay of the martensitic transition from the cubic phase to the rhombohedral phase upon cooling of the sample. The nanostructured ceramic materials are characterized by a high mechanical strength and unusually close values of the activation energies for bulk and grain-boundary electrical conduction.     

Facile preparation of Ag<Subscript>2</Subscript>V<Subscript>4</Subscript>O<Subscript>11</Subscript> nanoparticles via low-temperature molten salt synthesis method

Nanosized Ag₂V₄O₁₁ powders have been prepared via the low-temperature molten salt method using LiNO₃ as a reaction medium. The powders have been characterized by x-ray diffraction and transmission electron microscopy. The discharge properties of the powders have been assessed by the galvanostatic discharge test using CR2016 coin cells. The powder made at 300°C for 2 h is composed of nearly spherical particles about 40 nm in size. The discharge test shows that the powders prepared by the low-temperature molten salt method exhibit high discharge capacities.     

Preparation,crystal structure,and electrical conductivity of the solid electrolyte Zr<Subscript>0.86</Subscript>Sc<Subscript>0.12</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>1.93</Subscript>

The solid electrolyte Zr_0.88Sc_0.12Y_0.02O_1.93 for reduced-temperature SOFCs has been characterized by Rietveld X-ray powder diffraction analysis and conductivity measurements in the temperature range 295–970 K. Gas-tight nanostructured ceramic composites consisting of cubic, rhombohedral, and monoclinic phases have been produced by reaction sintering of mechanochemically prepared powders. The oxygen ion conductivity of the ceramic prepared by sintering at 1630 K, with a relative density of 94%, is three times lower than that of ceramics fabricated from DKKK Zr_0.89Sc_0.1Ce_0.01O_1.95 powder, but raising the sintering temperature to 1670 K increases the density of the ceramic to 99%, and its conductivity reaches the level of the DKKK ceramics. The core-shell ceramic nanocomposite obtained in this study possesses high mechanical strength and a reduced activation energy for grain-boundary conduction.     

Microwave-assisted hydrothermal synthesis of fine BaZrO<Subscript>3</Subscript> and BaHfO<Subscript>3</Subscript> powders

Fine BaZrO₃ and BaHfO₃ powders have been prepared by a microwave-assisted hydrothermal (MWHT) process. The powders have been characterized by x-ray diffraction and scanning electron microscopy, and their particle size distribution has been assessed from dynamic light scattering data. The results indicate that microwave processing during hydrothermal synthesis notably reduces the average particle size of the resulting powder and ensures a narrower particle size distribution. BaHfO₃ particles prepared under the optimal MWHT synthesis conditions are predominantly spherical in shape and uniform in size, with an average size (1.2 μm) a factor of 2.5 smaller in comparison with particles prepared by a conventional hydrothermal process (2.9 μm).     

Synthesis of Mg<Subscript>2</Subscript>Ni nanoparticles in a KCl-NaCl-MgCl<Subscript>2</Subscript> melt

The reaction between magnesium and nickel powders in a KCl-NaCl-MgCl₂ ionic melt at 970 K (reaction time, 5 h) has been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, and chemical analysis. According to scanning electron microscopy data, the synthesized Mg₂Ni powder consists of particles 70–75 nm in size, in reasonable agreement with the equivalent particle diameter, ≃ 64 nm, determined from the specific surface area of the Mg₂Ni powder and with the crystallite size, D _hkl ≃ 65 nm, evaluated from X-ray diffraction data. The hydrogen sorption properties of the Mg₂Ni obtained in a KCl-NaCl-MgCl₂ ionic melt are identical to those of Mg₂Ni powder prepared by a standard method, but the former reacts with hydrogen far more rapidly.     

Low-temperature synthesis of Sr<Subscript>0.3</Subscript>Ba<Subscript>0.7</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> ultrafine powder and its characteristics

Ultrafine strontium barium niobate (Sr_0.3Ba_0.7Nb₂O₆, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO₃)₂, Ba (NO₃)₂, NbF₅, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature (1 kHz) was found to be 930 and below 0.025.     

Novel synthesis and electrochemical properties of Mn(VO<Subscript>3</Subscript>)<Subscript>2</Subscript> as a high capacity electrode material in lithium-ions batteries

Mn(VO₃) powders was successfully synthesized by an effective and simple route-rheological phase reaction method and investigated as a cathode material for lithium-ion batteries. The structures, morphologies, phase purity of the prepared powder were characterized by X-ray diffraction, transmission electron microscope and X-ray photo-electron spectrometry, respectively. The results showed that the different heat temperatures could influence the particle size and crystallinity of the product. The charge-discharge experiments were performed to investigate the electrochemical properties of Mn(VO₃)₂ powder at a constant current density of 1.0 mA/cm² in a potential range of 0.0 and 3.5 V. The discharge capacity (441.1 mAh/g) showed only 31.7% losses of the initial discharge capacity (645.9 mAh/g) after 40 cycles.     

Magnetic and microwave-absorbing properties of SrAl<Subscript>4</Subscript>Fe<Subscript>8</Subscript>O<Subscript>19</Subscript> powders synthesized by coprecipitation and citric- combustion methods

Al-substituted M-type hexaferrite is a highly anisotropic ferromagnetic material. In the present study, the coprecipitation and the citric-combustion methods of synthesis for SrAl₄Fe₈O₁₉ powders were explored and their microstructure, magnetic properties, and microwave absorptivity examined. X-ray diffraction (XRD), scanning electron microscopy (SEM), a vibrating sample magnetometer, and a vector network analyser were used to characterize the powders. The XRD analyses indicated that the pure SrAl₄Fe₈O₁₉ powder was synthesized at 900°C and 1000°C for 3 h by coprecipitation, but only at 1000°C for the citric-combustion processes. The SEM analysis revealed that the coprecipitation process yielded a powder with a smaller particle size, near single-domain structure, uniform grain morphology, and smaller shape anisotropy than the citric-combustion process. The synthesis technique also significantly affected the magnetic properties and microwave-absorptivity. Conversely, calcining temperature and calcining time had less of an effect. The grain size was found to be a key factor affecting the property of the powder. The powders synthesized by coprecipitation method at calcining temperature of 900°C exhibited the largest magnetization, largest coercivity, and best microwave absorptivity.     

A study of S-doped TiO<Subscript>2</Subscript> for photoelectrochemical hydrogen generation from water

Sulfur-doped titanium dioxide (TiO₂) was investigated as a potential catalyst for photoelectrochemical hydrogen generation. Three preparation techniques were used: first ballmilling sulfur powder with Degussa P25 powder (P25), second, ball milling thiourea with P25, and third a sol–gel technique involving titanium (IV) butoxide and thiourea. The resulting powders were heat-treated and thin-film electrodes were prepared. In all three cases, the heat-treated powders contained small amounts of S (1–3%). However, Rietveld analysis on X-ray diffraction (XRD) measurements revealed no significant changes in lattice parameters. For the samples prepared using thiourea, X-ray photoelectron spectroscopy (XPS) measurements indicated the presence of N and C in the heat-treated powders in addition to S. In all cases, visible-ultraviolet spectroscopy performed on bulk powders confirmed the extension of absorption into the visible region. However, the same spectroscopic technique performed on thin-film electrodes (∼0.5 μm) suggests that the absorption coefficients were very small in the visible region (≤10⁴ m⁻¹). The first and third methods yielded powders with substantially smaller photocatalytic activity relative to P25 powder in the UV region. The electrodes prepared from powders obtained using the second method yielded photocurrents comparable to those prepared from P25 powder.     

Crystal structure and electrical properties of CaNaBi<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramics

Monophasic CaNaBi₂Nb₃O₁₂ powders were synthesized via the conventional solid-state reaction route. Rietveld refinement of the X-ray powder diffraction (XRD) data and selected area electron diffraction (SAED) studies confirmed the phase to be a three-layer Aurivillius oxide associated with an orthorhombic B2cb space group. The dielectric properties of the ceramics have been studied in the 300–800 K temperature range at various frequencies (1 kHz to 1 MHz). A dielectric anomaly was observed at 676 K for all the frequencies corresponding to the ferroelectric to paraelectric phase transition as it was also corroborated by the high temperature X-ray diffraction studies. The incidence of the polarization–electric field (P vs. E) hysteresis loop demonstrated CaNaBi₂Nb₃O₁₂ to be ferroelectric.     

Mechanochemical synthesis and characterization of Ni<Subscript>25</Subscript>Te<Subscript>75</Subscript> nanocrystalline alloy

Ni₂₅Te₇₅ nanocrystalline alloy containing trigonal NiTe₂ and Te nanocrystals was prepared through mechanochemical processing of pure elemental tellurium and nickel powders in argon atmosphere. The Ni₂₅Te₇₅ samples processed from 3 h to 30 h milling times were characterized by X-ray powder diffraction, transmission electron microscopy, magnetization and Raman spectroscopy. Trigonal NiTe₂ crystals with average size of 16 nm can be obtained after only 3 h of processing time. For longer milling times, the trigonal NiTe₂ phase becomes majority (about 70% with 30% for nanometric Te and no pure Ni was detected) and its average crystallite size slightly increases to 20 nm. Transmission electron microscopy images and electron diffraction patterns confirm the nanometric size of the crystalline domains in the agglomerated particles. The magnetic properties of the Ni₂₅Te₇₅ powders are dependent on synthesis time, suggesting a paramagnetic behavior mainly associated with the NiTe₂ nanophase. Raman spectra showed peaks that can be associated with unreacted Te and tellurium oxides modes, but it also showed several modes that can be attributed to trigonal NiTe₂ nanophase. The high-pressure experiments showed no phase transitions for NiTe₂ up to 17 GPa and Te phase transitions from form I to forms II and III occurred simultaneously at 4.5 GPa, remaining up to 12 GPa; after that, only reflections of Te-III and the NiTe₂ were observed. All the phase transitions observed with pressure are reversible after decompression. The bulk modulus determined from the least-squares fit of first-order Murnaghan equation of states is 110 GPa for the NiTe₂ nanophase and 28 GPa for Te-I.     

High voltage SnO<Subscript>2</Subscript> varistors prepared from nanocrystalline powders

In this study, SnO₂-based varistors were prepared from mechanically activated nanocrystalline powders. Nanocrystalline powders were derived by subjecting the initial powders to intensive high-energy activation with different times and ball to powder ratio. The effect of activation parameters on the powder properties and sintering temperature, as well as microstructural, micro-electrical and macro-electrical properties of the final specimens was evaluated. Varistors derived from high-energy mechanical activation exhibit a higher density (98.3% relative density) and more refined microstructure upon sintering at 1,300 °C in comparison varistors prepared from conventional powders. Breakdown voltage and nonlinear coefficient were increased up to 24 kV/cm and 45 respectively.     

Synthesis and microstructure of nanocrystalline Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> powders

Nanocrystalline ytterbia powders have been synthesized using different precursors prepared by precipitation from nitrate solutions: ytterbium carbonates, oxalates, and hydroxides. The powders have been characterized by X-ray diffraction and scanning electron microscopy. The nature of the precursor has no effect on the crystallization temperature of ytterbia but influences its microstructure. The particles range in shape from spherical to platelike. The average crystallite size of the Yb₂O₃ powders is 20–25 nm. Raising the heat-treatment temperature from 600 to 1000°C increases the crystallite size to 33–46 nm. The highest thermal stability is offered by the ytterbia powders prepared through carbonate decomposition.     

Synthesis by the solution combustion process and magnetic properties of iron oxide (Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) particles

This article describes the solution combustion synthesis technique as applicable to iron oxide powder production using urea as fuel and ferric nitrate as an oxidizer. It focuses on the thermodynamic modeling of the combustion reaction under different fuel-to-oxidant ratios. X-ray diffraction showed magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) phase formations for the as-synthesized powders. The smallest crystallite size was obtained by stoichiometric chemical reaction. The magnetic properties of the samples are also carefully discussed as superparamagnetic behavior.     

Preparation of apatite-type La<Subscript>9.33</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>6</Subscript>O<Subscript>2</Subscript> electrolyte by urea-nitrates combustion

Apatite-type La_9.33(SiO₄)₆O₂ powders have been prepared by urea-nitrates combustion at low temperature. Process parameters of combustion and characteristics of electrolyte were studied and optimized. Gelation time of precursor has been shortened distinctly by introducing an appropriate solvent system. Molar ratio of nitric acid to lanthanum oxide dependence of the nature of the phases has first been characterized. Well-crystallized La_9.33(SiO₄)₆O₂ powders with an average size of 30.5 nm were obtained at a calcining temperature as low as 800°C for 12h. Dense ceramic with a relative density of 96% was prepared by sintering the green compact of these nanopowders at 1400°C for 3 h. The sintering body exhibited a high ionic conductivity of 4.38 × 10⁻³ S/cm at 700°C.     

Physical properties of lead-free BaFe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> ceramics obtained from mechanochemically synthesized powders

Modern electronics expect functional materials that are eco-friendly and are obtained with lower energy consumption technological processes. The multiferroic lead-free BaFe_1/2Nb_1/2O₃ (BFN) ceramic powder has been prepared by mechanochemical synthesis from simple oxides at room temperature. The development of the synthesis has been monitored by XRD and SEM investigations, after different milling periods. The obtained powders contain large agglomerates built by crystals with an estimated size about 12–20 nm depending on the period of milling. From this powder, the multiferroic BFN ceramic samples have been prepared by uniaxial pressing and subsequent sintering pressureless method. The morphology of the BFN ceramic samples strongly depends on high-energy milling duration. The properties of the ceramic samples have been investigated by dielectric spectroscopy, in broad temperature and frequency ranges. The high-energy milling of the powders has strongly affected the dielectric permittivity and dielectric loss of the BaFe_1/2Nb_1/2O₃ ceramic samples. The usage of the mechanochemical synthesis to obtain the multiferroic lead-free BFN materials reduces the required thermal treatment and simultaneously improves the parameters of the BFN ceramics.     

A simple gel route to synthesize nano-Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> as a high-performance anode material for Li-ion batteries

Nano-Li₄Ti₅O₁₂ powders were synthesized by a simple gel route with acrylic acid, tetrabutyl titanate, and lithium nitrate as the precursors that were made into gels through thermal polymerization. The Li₄Ti₅O₁₂ powders were obtained by calcination of the gels at 700, 750, and 800 °C. They were characterized by thermal gravimetric analysis, differential thermal analysis, X-ray diffraction, and field emission scanning electron microscopy. The electrochemical performance of these nano-Li₄Ti₅O₁₂ powders was examined with galvanostatic cell cycling. The average particle size of the 700-, 750-, and 800 °C-calcined powders is about 70, 120, and 400 nm, respectively. The 750 °C-calcined powder exhibits a high capacity of over 160 mAh/g after 100 cycles and a good rate capability with a capacity of 122 mAh/g even at 10C rate.     

Dielectric properties of Pb(Zn<Subscript>1/3</Subscript>Ta<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-introduced (Ba,Pb)TiO<Subscript>3</Subscript> ceramic system

Ceramic powders of the Pb(Zn_1/3Ta_2/3)O₃-introduced BaTiO₃–PbTiO₃ system were prepared using a B-site precursor method. Perovskite formation tendencies of the system compositions were determined by X-ray diffraction. Weak-field low-frequency dielectric properties of the sintered ceramics were investigated. Dielectric constant spectra were further analyzed in terms of diffuseness. Internal microstructures of the ceramics were also examined.     

A facile synthesis of ZnS nanocrystallites by pyrolysis of single molecule precursors,Zn (cinnamtscz)<Subscript>2</Subscript> and ZnCl<Subscript>2</Subscript> (cinnamtsczH)<Subscript>2</Subscript>

ZnS nanocrystallites were synthesised by pyrolysis method using Zn (cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ (cinnamtsczH = cinnamaldehyde thiosemicarbazone) as single source precursors. The prepared ZnS nanocrystallites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, UV-Vis and fluorescence spectroscopy. The peak broadening in XRD and emission at shorter wavelength in fluorescence spectra showed the presence of nanocrystallites. The blue shift in UV-Vis absorption spectroscopy also proved the formation of nanocrystallites. TEM images show presence of plate-like and spherical ZnS nanoparticles obtained from Zn(cinnamtscz)₂ and ZnCl₂ (cinnamtsczH)₂ respectively.     

Low-temperature sintering of SiC reticulated porous ceramics with MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> additives as sintering aids

SiC reticulated porous ceramics (SiC RPCs) was fabricated with polymer replicas method by using MgO–Al₂O₃–SiO₂ additives as sintering aids at 1,000∼1,450 °C. The MgO–Al₂O₃–SiO₂ additives were from alumina, kaolin and Talc powders. By employing various experimental techniques, zeta potential, viscosity and rheological measurements, the dispersion of mixed powders (SiC, Al₂O₃, talc and kaolin) in aqueous media using silica sol as a binder was studied. The pH value of the optimum dispersion was found to be around pH 10 for the mixtures. The optimum condition of the slurry suitable for impregnating the polymeric sponge was obtained. At the same time, the influence of the sintering temperature and holding time on the properties of SiC RPCs was investigated. According to the properties of SiC RPCs, the optimal sintering temperature was chosen at 1,300 °C, which was lower than that with Al₂O₃–SiO₂ additives as sintering aids.